1. Field of the Invention
The invention relates to a friction clutch for motor vehicles.
2. Description of the Related Art
Conventional friction clutches for motor vehicles use a diaphragm spring to generate a force which clamps the clutch disk or friction disk between a pressure plate and a mating plate, which is usually designed as a flywheel. The characteristic force-distance curve of the diaphragm spring is such that the spring force initially rises to a maximum, falls to a minimum, and subsequently increases again as the spring travel of the diaphragm spring increases. To maintain a consistent spring force for each actuation of the clutch, the same section of the force-distance curve of the diaphragm spring should be used each time the clutch is operated. Various ways to compensate for the misalignment of that section of the spring characteristic curve which is used during operation of the friction clutch have been tried. The misalignment usually occurs when friction linings or friction disks of conventional friction clutches become worn such that the operating position of the diaphragm spring changes.
In multidisk clutches such, for example, as those according to German reference DE 195 45 972 A1, which are subjected to high thermal loads in sports car construction, the pressure plate is customarily replaced when the thickness of the set of disks is reduced as they become worn. However, this replacement operation requires a high servicing cost outlay because it entails removing the friction clutch.
Another German reference DE 43 06 505 discloses a single-disk friction clutch in which an automatically operating wear compensation device is arranged in the pressure force path between the diaphragm spring and the pressure plate. The wear compensation device comprises wedges which can be displaced in the circumferential direction of the diaphragm spring by a spring element. The wedges retain their position relative to one another as long as they are pressed against one another by the diaphragm spring. However, in the event of wear to the friction linings of the clutch disk of this clutch, the wedges fill up the increasing distance between the pressure plate and the diaphragm spring by being displaced toward one another under the action of the spring element. Ventilating distance-limiting elements are frictionally locked in an axial bore in the pressure plate. Ventilating springs act on the pressure plate counter to the pressure of the diaphragm spring, but the ventilating distance-limiting elements are arranged in such a manner that they can be displaced counter to the locking force. In the engaged position of the clutch, the ventilating distance-limiting elements butt against the flywheel which is clamping the friction linings between itself and the pressure plate. In the disengaged position, the ventilating distance-limiting elements limit the ventilating distance of the pressure plate by butting against the clutch housing. When wear occurs on the friction linings of the clutch disk, the ventilating distance-limiting members are displaced relative to the pressure plate counter to their locking force. Similar prior art friction clutches with automatically operating compensation device are also known from German references DE 29 20 932 C2, DE 42 39 289 A1 and DE 35 18 781 A1.
Yet another German reference DE-B 1,286,839 discloses an electromagnetically actuable multidisk clutch in which the thickness of the set of friction disks, which is to be pressed against a shoulder of the magnet body by an armature plate of the electromagnet, is balanced by a wear compensation device. The wear compensation device comprises stepped rings which are concentric with respect to the friction disks and rotate under the action of a tension spring as the wear increases to counteract the wear-related reduction in the thickness of the set of disks. The stepped rings are arranged on that side of the set of disks which is remote from the armature plate so that the distance of the armature plate from the poles of the electromagnet is constant. A resilient latching disk is guided on a bolt which extends in the lifting direction of the armature plate. The latching disk is displacable counter to a latching force of predetermined magnitude of the stepped ring which is close to the armature plate. The latching disk rests between two ventilating distance-limiting stops of the armature plate, which is preloaded in the disengagement direction by a compression spring, such that the latching disk limits the ventilating clearance of the armature plate to a predetermined value which is independent of the wear condition of the friction disks.